The present invention relates to a circulating water pool which can be used as a pool for learning how to swim and for intensified training of swimming players on the advice of an instructor or the like or as model testing tank for investigating and measuring various hydrodynamic factors of ship and off-structure models.
Scientific and efficient methods have been recently employed in swimming training. There have been proposed and demonstrated some circulating water type pools in which a device for flowing water is disposed in a vertical type circulating water passage having an observation window portion so that one can observe and advice a beginner who wants to learn how to swim and a trainee.
FIG. 1 illustrates one example of the conventional circulating water pools. A vertical circulating water pool main body 1 which is mounted on a foundation 2 comprises an upper water passage 3, a lower water passage and front and rear curved portions 5 and 6 which deflect the direction of the water flow and intercommunicate between the upper and lower water passage 3 and 4. A side wall of the pool main body 1 has a plurality of observation windows 7 along the upper water passage 3 which is opened upwardly and has a free water surface, whereby an observation section is defined. An impeller 9 for producing the water flow circulating the upper and lower water passage 3 and 4 is disposed in the lower water passage 4 in the vicinity of its upstream end or the rear curved water passage 6 and is driven by drive device 10 disposed outside of the pool main body 1. Furthermore, guide vanes 11 are securely disposed in the front and rear water flow deflection portion 5 and 6 in order to change the direction of the water flow.
When the impeller 9 is driven by the drive device 10, the water flow is produced and accelerated in the low water passage 4 and is changed in direction in the front curved portion 5 so as to enter the upper passage 3. Thereafter the water flow leaving the upper water passage 3 is again changed in direction by the rear curved portion 6 and sucked into the lower water passage 4 by the rotating impeller 9. Thus the water circulates through the pool main body 1.
In the conventional circulating water pool of the type described above, the front water flow deflection portion for changing the direction of the water flow flowing from the impeller has two square corners and short guide vanes 11 are disposed at each corner and spaced apart from each other by the same distance so that the water flow is forced to flow outwardly by the centrifugal force. In order to change such outwardly deflected water flow into the uniform water flow throughout the upper water passage 3 where the observation section 8 is located for instance as shown in FIG. 1, a pressure chamber 12 having a three-dimensionally curved surfaces is formed at the upstream end of the upper water passage 3 and a nozzle-shaped portion extending upwardly from the upper surface of the pressure chamber 12 is communicated with a vacuum pump 13 to suck water so that no free water surface exists in the pressure chamber 12.
However, when the circulating water pool is arranged in the manner described above, a part of the upper water passage 3 along the length of the observation section 8 has a free water surface in contact with the surrounding atmosphere so that the pressure between the water flow having a free water surface and the water in the pressure chamber 12 becomes discontinuous, resulting in the standing or stationary waves produced in the upper water passage 3 along the observation section 8. Such standing or stationary waves, which are a fatal defect in the circulating water pools, must be decreased by disposing a wave-supressing plate 14 at the upstream end of the observation section 8. Then, because of the upwardly extending nozzle portion of the pressure chamber 12 and the wave-suppressing plate 14, a boundary layer generates to cause the flow rate drops by about 20% along the observation section 8. In order to compensate the decrease in flow rate, a surface accelerating device 15 must be disposed between the pressure chamber 12 and the wave-suppressing plate 14. As described above, in order to decrease the standing or stationary waves and to make the water flow uniform along the observation section 8 in the upper passage 3, the conventional circulating water pools must be provided with various complicated devices.
In order to solve the above-described problems, a circulating water pool as shown in FIG. 2 has been devised and demonstrated. The front and rear ends of the pool main body 1 are curved to define the curved water passages 5 and 6 and a round bulged portion 36 is formed at the upstream end of the bottom 3' of the upper water passage 3 so as to prevent the separation of the water flow passed through the front curved portion 5.
In the case of the circulation water pool with such curved water passages 5 and 6, the bulged portion 36 is effective to some extent to prevent the water flow separation; but a step is inevitably formed between the bulged portion 36 and the flat bottom 3' so that the reversal of the water flow results. Furthermore, because of variations in depth, the standing or stationary waves are produced over a free water surface or the uniform water flow through the section of the upper water passage 3 along the observation section 8 is considerably adversely affected.
The present invention was made to substantially solve the above and other problems encountered in the conventional circulating water pool and becomes more apparent from the following description of some preferred embodiments thereof taken in conjunction with the accompanying drawings.